A class AB amplifier includes a differential amplifier, a push-pull output stage, and a AB bias circuit. The push-pull output stage includes a p-type transistor and an n-type transistor that drive a signal to an output. The class AB bias circuit is configured to bias the push-pull output stage.
Accidental short-circuiting of the output is a problem for class AB amplifiers. If the output of the amplifier is accidentally shorted to ground, then the gate of the p-type transistor decreases in voltage, causing a significant increase in the output current. Similarly, if the output of the amplifier is accidentally shorted to the supply voltage, then the gate of the n-type transistor increases in voltage, causing a significant increase in the output current. The increased output current caused by the short circuit may damage the differential amplifier.